The present invention relates to a method for dyeing of natural leathers.
At present, natural leather materials are mainly dyed by acid dyestuffs, direct dyestuffs, basic dyestuffs, etc., however, the thus dyed leathers are not sufficient in alkaline fastness, wet fastness, etc., and a method for dyeing by using reactive dyestuffs has been also tried.
In the case of dyeing the natural leather materials with ordinary reactive dyestuffs having the reactive group(s) such as a monochlorotriazinyl group, a dichlorotriazinyl group, a monofluorotriazinyl group, a vinylsulfonyl group and the like, the acid-binder which is necessary for causing the reactive dyestuff to dye the leather material, or the substance which releases the acid-binder by heating, etc., for instance, sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, sodium metasilicate, trisodium phosphate, tripotassium phosphate, potassium pyrophosphate, sodium pyrophosphate, sodium hydrogencarbonate, sodium trichloroacetate and the like spoils the physical properties (the strength, the touch, etc.) of the natural leather material therefore a method for dyeing of the natural leather materials with ordinary reactive dyestuffs did not carried out commercially. Moreover, in the case of dyeing the natural leathers by acid dyestuffs, direct dyestuffs or basic dyestuffs, a use of a large amount of inorganic electrolytes such as sodium chloride, sodium sulfate and the like is required, and such an inorganic electrolyte not only gives detrimental effects on the physical properties of the leather but also the use thereof is not economically profitable.
Accordingly, the development of a method for obtaining the dyed natural leather which are excellent in fastness, particularly in light fastness, alkaline-sweat fastness, and wet fastness by using a dyestuff not using any acid-binder which spoils the physical properties of natural leather, any substance which releases an acid-binder by heating, etc. nor any inorganic electrolyte which is economically unprofitable has been eagerly required.
As a result of the present inventors' studies for finding a dyeing method which may give excellent dyed natural leather without using any acid-binder or any substance which releases the acid-binder nor any inorganic electrolyte, the present invention has been attained.